Transition couplings



FlG.2

F I G. 6

INVENTOR. Hermon F. Buschow Dec. 13, 1966 FIG.|

FlG.3

FlG.4

FIG.5

Reissued Dec. 13, 1966 26,126 TRANSITION COUPLINGS Herman F. Buschow,Hiilsdale, N.J., assignor to Hydrocarbon Research, Inc., New York, N.Y.,a corporation of New Jersey Original No. 3,208,776, dated Sept. 28,1965, Ser. No. 54,286, Sept. 6, 1960. Application for reissue June 6,1966, Ser. No. 560,369

2 Claims. (Cl. 285-284) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

The present invention relates to a transition coupling of the type shownin the US. Patent 2,787,481 of which I am one of the inventors. Moreparticularly, the invention relates to a tubular coupling consisting oftwo dissimilar metallic nipples which permit field welding dissimilarpipes which are not normally weldable together.

It is known that aluminum and stainless steel or copper and stainlesssteel are not readily subject to welding in the field. Nevertheless, incryogenic service stainless steel elements are often used as a heat damto prevent heat flow from aluminum piping. There are many otheropportunities for the use of interconnected piping of dissimilarmaterials and I have found that the use of short transition couplingswhich may be preassembled are suitable to field Welding when they can bemade adequately gas tight and of sufficient mechanical strength to takeand transfer the normal longitudinal stress in a piping system. It isimportant that such a coupling should minimize maintenance due totemperature changes, and should be devoid of flanges which requirecomplicated bolts, gaskets, and similar attaching means.

In the past, I have found that a mechanically shrunk couplingconstruction to be satisfactory as it can be made mechanically strongand gas tight for most purposes by the steps discussed in the abovementioned patent. I have found, however, that such constructions requireconsiderable precision in the formation of the parts and carefultemperature control to permit the necessary relative expansion andcontraction for assembly. It does not lend itself to typical productionline construction.

I am aware of prior efforts of casting aluminum on ferrous membersprimarily for the purpose of heat exchange and such practice generallyincludes a preliminary dipping of the ferrous parts in an aluminum bath.However, unless carefully controlled, the intermediate ferroaluminumlayer which is formed is brittle and mechanically weak. Such aconstruction cannot be used safely in a piping system wherein anymovement of the pipes adjacent to the coupling would tend to break thegas tight seal and is particularly objectionable in piping which is incryogenic service.

It is the principal purpose of my invention to produce a coupling of thetransition type for field welding of piping of dissimilar metals theparts of the coupling being formed into a unit which is gas tight and ofsuch mechanical strength as to withstand the stresses of adjacentpiping.

More particularly, my invention relates to an improved transition pipeor tubular coupling, particularly for high pressure and low temperaturefluid service, which coupling is readily adapted to be Welded into apiping system and is substantially stronger and more positive in sealingthan prior available couplings of this type.

My invention also has for its object an improved method of makingtransition couplings, particularly of copper or stainless steel andaluminum wherein the method steps reduce costs and improve the strengthof the coupling.

Further objects and advantages of my invention will appear from thefollowing description of a preferred form of embodiment thereof taken inconnection with the attached drawing in which:

FIG. 1 is a central longitudinal cross section of one form of coupling.

FIG. 2 is a central vertical cross section through a fluxing bath.

FIG. 3 is a central vertical section through the mold.

FIG. 4 is an elevation, with parts in cross section, showing a modifiedform of coupling.

FIG. 5 is an elevational view, partly in section, of a still furthermodified form of coupling primarily for above zero degree Fahrenheitservice.

FIG. 6 is a partial central section, with parts in elevation of acoupling for valve service.

The coupling shown in FIG. 1 is adapted for use in the field welding ofdissimilar piping [using] such as aluminum and stainless steel which isused in cryogenic service with temperatures as low as 423 F. and withpressures in the order of 450 p.s.i.g. where gas leakage is limited totwo microns per cubic foot per hour. It consists of a stainless steelbase nipple 10 to which is attached an aluminum nipple 12. For mosteffective processing operations, the stainless steel may be of the l88type, and the aluminum is of a suitable alloy commonly designated as 35by the Aluminum Company of America. Other alloys that can be used are28; 61; or 63.

The stainless steel nipple 10, and the aluminum nipple 12 willpreferably have a smooth common bore generally indicated at 14. Toincrease the axial strength of the coupling as hereinafter described,the stainless steel nipple will also have one or more grooves or slots16 which may conveniently be of the order of 3/ of an inch in width, andabout 0.03 inch deep.

I now find that it is preferable, in the interest of rapid production,as well as permanence of gas scaling, to form the lighter aluminum alloyouter nipple 12 around (or against) the higher density steel innernipple 10 as by a casting operating as hereinafter described as suchpractice establishes a seal which is tight not only at all normalatmospheric temperatures, but improves in cryogenic service.

This construction of the coupling shown in FIG. 1 is accomplished by atleast six principal steps at follows:

(1) Clean the high density nipple to remove oil and dirt.

(2) Pre heat the high density (inner) nipple to about 50)600 F.

(3) Flux the high density (inner) nipple to remove oxides and to preheat it nearly to the aluminum melting point.

(4) Pour molten light aluminum or aluminum alloy metal into mold.

(5) Insert high density nipple in m-old.

(6) Cool assembly promptly.

As to step one, I have found that stainless steel nipples, particularlyafter storage, frequently have oil films or dirt which must be removedto permit an aluminum contact. I, therefore, normally clean the steelnipple with the usual dcgreasing techniques and I may take a shallow orbright cut without without necessarily removing the tool marks. Thisserves as a standard condition for the preliminary treatment of thenipple.

As a second step I find it desirable to preheat the nipple to aboutSOD-[166] 600 as by an induction heating coil or other means not shown.It is important that this preheating not exceed about 600 F. and in anyevent must be below 800 F. in air to prevent a reoxidation of the metalsurface.

As a third step in the process the nipple 10 is injected into a flux 20in the crucible 18. The flux used for stainless steel is primarily afluoride composition which I find is particularly effective in removingoxides such as chromic oxide. Preferably, the flux is maintained atabout 1000 F. by heating the container 18 to a somewhat highertemperature. The steel nipple is preferably moved up and down in theflux bath 20 after the nipple has substantially reached suchtemperature. It has been found that when the nipple is initially placedin the flux some solidification of the flux takes place forming a skinin the nature of a crud, and that when this crud redissolves in theflux, the nipple has reached the desired preheating temperature.Depending on the size of the couplings, this may take several minutes ormore.

As the fourth step in my processing, the molten light metal is nextpoured into the mold 24 which may be heated by well known means. Usuallythe temperature of the melt is around l400-1450 F. which is about twohundred degrees higher than the melting point. The stainless steelnipple 10 with some flux coating on its outer side is then inserted intothe melt and placed over a plug 22 in the sand mold 24 primarily toassure a uniform clearance with the inner walls of the mold and todiminish the amount of aluminum which would penetrate the interior ofthe nipple 10. It is, of course, entirely appropriate to coat theinternal bore of the nipple 10 as with graphite to prevent aluminumadhering to the internal surfaces.

Conveniently the nipple 10 may be tack welded as at 26 or clamped to themold cover 28 for centering over the core plug 22. The mold cover 28 maybe provided with guides 30 to engage the outer side of the mold box 32.

As a final step in my processing the aluminum is promptly cooled by thecontact with the colder ferrous element not only to cause an immediateshrinkage of the aluminum against the internal nipple and its slots butto reduce migration of aluminum and iron molecules which would otherwiseform an objectionable alloy layer.

While [some bone may] a thin bond will result, it [is incidental and] isto be minimized as much as possible. On large couplings for example Imay utilize internal cooling coils 34 in the sand mold through which asuitable coolant can be circulated. Normally, however, I find itsufficient to promptly withdraw the stainless steel nipple 10 and itsattached aluminum nipple from the mold 12 for air cooling.

A coupling of this type may then be suitably machined as indicated inFIG. 1 by providing suitable welding scarfs as is well known in theindustry.

I find that a coupling of this type is not only unusually gas tight andcorrosion free with a very low gas permeability at very low temperaturesbut will withstand considerable shock treatment as evidenced by tests ofrepeated heating and sudden cooling. It also withstands shear and has amechanical strength as great as or greater than the piping to which itis attached.

It will, of course, be appreciated that with the higher co-efficient ofexpansion of aluminum with respect to stainless steel, and the ratio forthese materials is nearly two to one, there is an inherent shrinkage asthe temperature drops below the initial casting temperature of 1400 F.Furthermore, as the normal operating temperature for such couplings maybe several hundred degrees below 0 F. the compression tends to increaseand further protect the seal.

There are occasions when couplings of this type are also desirable foroperating temperatures which may reach a super atmospheric condition forexample as high as about 400 F. In such case I prefer to utilize thecoupling more particularly shown in FIG. 4 which includes not only thestainless steel nipple 40 and the aluminum nipple 42 which has beenpoured over the stainless steel nipple in substantially the same manneras in FIGS. 1 to 3, but also to use a surrounding steel sleeve 44. Thismay be of truncated shape as at 44a and is conveniently welded to thenipple 40 as by the weld 46. It may also be integral with the stainlesssteel nipple 40.

In this construction it is convenient to insert the ele ment 40 afterfiuxing. into the aluminum which will flow into the pocket between theinner sleeve 40 and the outer sleeve 44 for permanent bonding of thealuminum thereto.

In this construction, it may be found desirable also to have one or moregrooves 48-on the exterior 44 of the nipple and a similar groove 50 onthe interior of the sleeve 40. The extra reinforcement in such aconstruction makes it possible to have a much shorter coupling for thesame operating temperatures and pressures.

If a coupling were only used for elevated temperatures of above zerodegrees F. as for example in steam service (up to about 400 F.) theinner sleeve 50 would not be needed. Such a construction as shown inFIG. 5 wherein the coupling generally shown at 60 has a stainless steelouter nipple portion 62 and an inner aluminum nipple portion 64 which issurrounded by the outer portion 62. In such case, as in the previouslydescribed forms, the central bore 66 is smooth and common to both nippleportions. Furthermore, each nipple portion 62 and 64 will normally havethe suitably formed end portions 62a and 64a respectively to permitsecuring, by welding, of adjacent pipe members. A shear rib 68 may beused if longitudinal shear becomes a problem of reinforcement.

In FIG. 6, I have shown a modified form of coupling which has thecharacteristics of a pipe but which has no fluid flow through it. Inthis construction, a valve body 70, of aluminum will have a butterflyvalve element 72 mounted on stem 74 which in turn is a part of valve rod76. This rod, conveniently of stainless steel, is intended to beoperated from a remote point to which cold should not flow. A shield ortube 78, also of stainless steel, similarly extends coextensively withthe valve rod 76. Usually such shield serves to permit the formation ofinsulation around the valve without interfering with its operation.

To conveniently secure the stainless steel shield to the aluminum valvebody 70, I form a coupling comprising a cast outer nipple or sleeve ofaluminum shown at on the valve shield. Thereafter it is a relativelysimple field welding matter to weld the two adjacent aluminum pieces (80and the valve body 70 as at 82). Such a construction becomes a completebarrier to cold flow and renders field assembly entirely simple andconvenient.

While stainless steel-aluminum couplings are in great demand, I alsofind it possible to use a copper base element instead of the stainlesssteel. In such case, the time of cooling of the aluminum is somewhatless than with the stainless steel. A different flux will also be used.

In view of the various modifications of the invention which will occurto those skilled in the art L] up-on consideration of the [foregone]foregoing disclosures without departing from the spirit or scope [theyare of] thereof, only such limitations [and] should be imposed as areindicated by the appended claims.

I claim:

I. A transition coupling for use in heat transfer systems comprising atelescoped pair of cylindrical nipples, the outer nipple and the innernipple being formed, respectively, of low density aluminum having a highcoefficient of heat transfer and a high density stainless steel having alow coefficient of heat transfer, said aluminum nipple being moldedaround the stainless steel nipple, said nipples extending axiaillybeyond the telescoped portions thereof in opposite directions to formconnecting portions adapted to be welded to portions of similar metalswhereby the stresses of said member are transferred through saidcoupling. the wall thickness of the low density nipple beingsubstantially greater than the wall thickness of the high density nippleand a chemical bond uniting said nipples at their interface, said bondbeing occasioned by the migration of iron from the stainless steel intothe alumin um forming an iron-aluminum alloy, said alloy being radiallymicroscopically thin and penetrating into the aluminum by radiallydecreasing amounts providing a cohesion between said nipples having arelatively low brittleness factor and serving as a gas seal.

2. A transition coupling for use in piping systems comprising a pair ofpre-assembled cylindrical members, said members being formed,respectively, of aluminum and steel, said aluminum member being moldedagainst the steel member, said members extending axially beyond theadjacent portions thereof in opposite directions to form connectingportions adapted to be welded respectively to portions of similar metalsof the piping system whereby the stressesof said piping system aretransferred through the coupling and a chemical bond uniting saidcoupling members at their adjacent portions, said bona being occasionedby the interm igration of the metals of the coupling members forming aferroaluminum alloy, said alloy being microscopically thin across theadjacent portions and penetrating into the adjacent members bydecreasing wmaunts providing a cohesion between said coupling membershaving a relatively low brittleness factor and serving as a gas seal.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS Monnot 22-204 X Mead 22--03 Austin 22-203 Kyle22-203 Boothman 285-329 Dick 285-331 Jacobson 285-287 Reynolds 22-204 XRoswell 251-308 Frantz 251-308 Schacfer et al. 22-203 X Buschow 285-329Hickman 285-173 Grenell 285-291 Hutchins 285-173 Jepson 29-257 Can ad-a.

CARL W. TOMLIN, Primary Examiner.

D. W. AROLA, Assistant Examiner.

